sheet metal

Sheet metal differs from “plate” in thickness, sheet being less than 1/8 inch thick (some say less than ¼ inch). Sheet metal is also expected to have a much better surface finish than plate.

Sheet metal is usually purchased by thickness. With the building of the first rolling mills (Wales, 18th century), manufacturers had to decide what series of thicknesses to offer. Some took their series from the series of diameters in wire gages; others made up their own gages. The use of many different gages led to confusion.

Iron and steel sheet

United States

By 1877, the American Institute of Mining Engineers was recommending a Standard Decimal Gage, in which the gage numbers were simply the thickness of the sheet in thousandths of an inch. The series ran 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 25, 28, 32, 36, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 110, 125, 135, 150, 165, 180, 200, 220, 240, and 250.

An act of Congress, March 3, 1893, established the U.S. Standard Gauge for sheet iron and steel for the purpose of levying taxes and duties. This series was not based on thickness, but mass. The mass of a cubic foot of wrought iron was taken to be 480 pounds avoirdupois. A sheet 1 foot by 1 foot by 1 inch thick will then weigh 40 pounds, or 640 ounces, so a sheet 1/640 inch thick should weigh 1 ounce per square foot. The gage numbers started at 7/0, which was set at 320 ounces per square foot (and thus 320/640 = ½ inch thick). From #7/0 to #0 the gages differed by 20 ounces (so in thickness by approximately twenty 640ths); from #0 to #14, ten ounces (and ten 640ths); from #14 to #16, five ounces; from #16 to #20 four; from #20 to #26 two; #26 to #31 one; #31 to #36, half an ounce, and #36 to #38, a quarter of an ounce.

This provided unsatisfactory, not least because it was based on wrought iron and not rolled steel, whose weight is nearer 501.84 pounds per cubic foot. In 1895 the ASME and the American Railway Master Mechanics Association jointly called for the use of the decimal gage and “the abandonment and disuse of the other gauges now in use, as tending to confusion and error.” Thereafter the decimal gage was often referred to as the “Master Mechanics Gage.” Westinghouse Electric & Mfg. made the most famous attempt to abandon gage numbers (American Machinist Apr 14, 1904).

But gage numbers would not die. The steel manufacturers redefined the U. S. Standard gage numbers, retaining the weights per square foot, but correcting the thickness for the weight of continuously rolled steel. This became known as the Manufacturers' Standard Gage, in which #16 sheet, for example, still weighed 40 ounces per square foot, but was 0.0598" thick instead of the 1/16" (= 40/640" = 0.0625") expected by the U.S. Standard Gage. (The actual specification includes a tolerance of plusmn; 0.005 to 0.007", depending on the width of the roll and whether it was hot rolled or cold rolled.)

Aluminum, copper, magnesium

In the USA, the Brown and Sharpe Gage, also called the American Wire Gage, is used for most nonferrous sheet metal, including aluminum, brass, German silver, magnesium, and phosphor bronze sheet. In Britain the Imperial Wire gauge was used for aluminum (or should we say aluminium) sheets and the Birmingham Metal Gage (not to be confused with the Birmingham Gage or the Birmingham or Stub's Iron Wire Gage) for brass sheets.

Zinc

Zinc has a gauge all its own.

Sheet Metal Gauges
Gauge No. Manuf.
Standard
Gauge
Brown &
Sharpe
Gauge
Birmingham
Wire
Gauge
Birmingham
Sheet Metal
Gauge
1914
Imperial
Wire
Gauge
Zinc
Gauge
15/0 1.000
14/0 0.9583
13/0 0.9167
12/0 0.8750
11/0 0.8333
10/0 0.7917
9/0 0.7500
8/0 0.7083
7/0 0.6666 0.5000
6/0 0.5800 0.6250 0.4640
5/0 0.5165 0.500 0.5883 0.4320
4/0 0.4600 0.454 0.5416 0.4000
3/0 0.4096 0.425 0.5000 0.3720
00 0.3648 0.380 0.4450 0.3480
0 0.3249 0.340 0.3964 0.3240
1 0.2893 0.300* 0.3532 0.3000 0.002
2 0.2576 0.284 0.3147 0.2760 0.004
3 0.2391 0.2294 0.259* 0.2804 0.2520 0.006
4 0.2242 0.2043 0.239 0.2500 0.2320 0.008
5 0.2092 0.1819 0.220* 0.2225 0.2120 0.010
6 0.1943 0.1620 0.203* 0.1981 0.1920 0.012
7 0.1793 0.1443 0.180* 0.1764 0.1760 0.014
8 0.1644 0.1285 0.165* 0.1570 0.1600 0.016
9 0.1495 0.1144 0.148* 0.1398 0.1440 0.018
10 0.1345 0.1019 0.134* 0.1250 0.1280 0.020
11 0.1196 0.09075 0.120* 0.1113 0.1160 0.024
12 0.1046 0.0808 0.109 0.0991 0.1040 0.028
13 0.0897 0.0720 0.095 0.0882 0.0920 0.032
14 0.0747 0.0641 0.083 0.0785 0.0800 0.036
15 0.0673 0.0571 0.072 0.0699 0.0720 0.040
16 0.0598 0.0508 0.065 0.0625 0.0640 0.045
17 0.0538 0.0453 0.059* 0.0556 0.0560 0.050
18 0.0478 0.0403 0.049 0.0495 0.0480 0.055
19 0.0418 0.0359 0.042 0.0440 0.0400 0.060
20 0.0359 0.0320 0.035 0.0392 0.0360 0.070
21 0.0329 0.0285 0.032 0.0349 0.0320 0.080
22 0.0299 0.0253 0.028 0.03125 0.0280 0.090
23 0.0269 0.0226 0.025 0.02782 0.0240 0.100
24 0.0239 0.0201 0.022 0.02476 0.0220 0.125
25 0.0209 0.0179 0.020 0.02204 0.0200 0.250
26 0.0179 0.0159 0.018 0.01961 0.0180 0.375
27 0.0164 0.0142 0.016 0.01745 0.0164 0.500
28 0.0149 0.0126 0.014 0.01562 0.0148 1.000
29 0.0135 0.0113 0.013 0.01390 0.0136
30 0.0120 0.0100 0.012 0.01230 0.0124
31 0.0105 0.0089 0.010 0.01100 0.0116
32 0.0097 0.0080 0.009 0.00980 0.0108
33 0.0090 0.0071 0.008 0.00870 0.0100
34 0.0082 0.0063 0.007 0.00770 0.0092
35 0.0075 0.0056 0.005 0.00690 0.0084
36 0.0067 0.0050 0.004 0.00610 0.0076
37 0.0064 0.0045 0.00540 0.0068
38 0.0060 0.0040 0.00480 0.0060
39 0.0035 0.00430 0.0052
40 0.00386
41 0.00343
42 0.00306
43 0.00272
44 0.00242
45 0.00215
46 0.00192
47 0.00170
48 0.00152
49 0.00135
50 0.00120
51 0.00107
52 0.00095

* In the 19th century, several different tables defining the “Birmingham Wire Gauge” were in circulation. For the sizes marked with an asterisk, Molesworth's Engineering Formulae gives: 1 = 0.312″, 3 = 0.261″, 5 = 0.217″, 6 = 0.208″, 7 = 0.187″. 8 = 0.166″, 9 = 0.158″, 10 = 0.137″, 11 = 0.125″, 17 = 0.056″.